This invention relates to analog signal processing, and more particularly to radio systems.
This invention further relates to the transceiver and components thereof described and claimed in the following U.S. Patent Applications filed of even date with an assigned to the assignee of the present invention: U.S. Ser. No. 791,611 entitled "A Digitally Transmitting Transceiver" by Edward R. Caudel and William R. Wilson; U.S. Ser. No. 791,629 entitled "A Clarifying Radio Receiver" by Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,264 entitled "An Electronic Phase Locked Loop" by Michael J. Cochran; U.S. Ser. No. 791,450 entitled "A Transceiver With Only One Reference Frequency" by Michael J. Cochran; U.S. Ser. No. 791,265 entitled "A Signal Strength Measuring Tranceiver" by Edward R. Caudel; U.S. Ser. No. 791,614 entitled "A Charge Transfer Device Radio System" by Michael J. Cochran; U.S. Ser. No. 791,253 entitled "A Transceiver Capable of Sensing a Clear Channel" by Jerry D. Merryman, Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,256 entitled "A Highly Selective Programmable Filter Module" by Michael J. Cochran and Edward R. Caudel; and U.S. Ser. No. 791,616 entitled "A Dual Processor Transceiver" by Edward R. Caudel, William R. Wilson and Thomas E. Merrow. Such copending patent applications are hereby incorporated herein by reference. Radio systems receive radiated electronic input signals comprised of a plurality of non-overlapping frequency bends, filter a selectable band from the plurality, frequency shift the filtered band from radio frequencies to a lower frequency, and convert the selected band to audible sounds. The input signals may be amplitude modulated (AM), or signal sideband (SSB) signals as an example. Antenna means receive the radiated input signals. Filtering devices are included in the radio system to select one of the bands from the plurality. Mixing devices are included to frequency shift the selected band. And demodulator devices are included to demodulate the selected band.
In the past, single sideband signals have been particularly troublesome to receive with clarity. The problem arises because sideband signals have no carrier to lock onto to aide in demodulation. And demodulation is made more difficult because transmitters which send signals sideband signals are not required to align the signals with a fixed reference frequency, but only are required to place the sideband signals somewhere within a frequency channel. Thus, the receiving system is required to demodulate the sideband signals regardless of where they lie within their respective channel. This requirement is known in the art as the clarifying function of a receiver.
Prior art receivers perform the clarifying function by hand tuning. For example, the receiver operator manually adjusted the frequency of a mixing clock signal by turning a control knob. In response thereto, the frequency of a mixing clock signal was either increased or decreased until the speaker output produced clearly sounding audible tones. By comparison, the present invention performs the clarification without manual intervention. This is achieved by a transceiver having means for transmitting sideband signals which include an intermittently present carrier. The transceiver further includes frequency measuring means which are operable in the receive mode to detect the frequency of an intermittently transmitted carrier. After comparing the nominal frequency of the transmitted carrier to the actual carrier frequency measured, the disclosed invention automatically compensates for any frequency difference by appropriately adjusting a clocking frequency for the receive circuitry.
Accordingly, it is one object of the invention to provide an improved single sideband radio system.
It is another object of the invention to provide a sideband transmitter capable of transmitting sideband signals including therein an intermittent carrier frequency.
It is another object of the invention to provide a sideband transmitter which transmits a carrier frequency for a short interval just prior to transmitting sideband signals.
It is another object of the invention to provide a sideband receiver capable of detecting a carrier frequency which is present for intermittent time intervals in a sideband signal.
It is another object of the invention to provide a sideband receiver capable of automatically clarifying sideband signals.
It is still another object of the invention to provide a sideband receiver having a microprocessor for automatically generating micro-commands indicating a selectable frequency that clarifies a received sideband signal.